Selenium bioavailabilty higher from Brazil nuts, says study

By Stephen Daniells, 15-Feb-2008

Consuming only two Brazil nuts every day can raise blood selenium levels by about 65 per cent, suggests a new study from New Zealand

Results of the randomised controlled trial showed that the bioavailability of the mineral from the nuts was higher than from selenomethionine, one of the most common forms used for fortifying foods and in dietary supplements.

“Inclusion of this high-selenium food in the diet could avoid the need for fortification or supplements to improve the selenium status of New Zealanders,” wrote lead author Christine Thomson from the University of Otago.

The study, published in this month’s American Journal of Clinical Nutrition, could also boost the nut as a functional food ingredient in Europe where selenium levels have been falling since the EU imposed levies on wheat imports from the US, where soil selenium levels are high.

As a result, average intake of selenium in the UK has fallen from 60 to 34 micrograms per day, leading to calls from some to enrich soil and fertilizers with selenium to boost public consumption.

The European recommended daily intake (RDI) is 65 micrograms.

The new study, performed with 59 New Zealand adults, compared blood levels of selenium after consuming two Brazil nuts estimated to provide a 100 microgram dose of selenium, selenomethionine giving a known dose of 100 micrograms of the mineral, or placebo every day for 12 weeks. The actual daily dose of selenium from the nuts averaged 53 micrograms, said the researchers.

At the end of the study, Thomson and co-workers found that blood levels of selenium had increased by 64.2, 61.0, and 7.6 per cent among subjects in the Brazil nuts, selenomethionine, and placebo groups, respectively.

Moreover, blood levels of glutathione peroxidase (GPx) – an antioxidant enzyme that is dependent on selenium to function properly – had increased by 8.3 and 3.4 per cent in the Brazil nuts and selenomethionine groups, respectively, while a 1.2 per cent decrease in levels was observed in the placebo group.

“Change over time at 12 weeks in plasma selenium and plasma GPx activity in the Brazil nut and selenomethionine groups differed significantly from the placebo group but not from each other,” stated the researchers.

“The change in whole blood GPx activity was greater in the Brazil nut group than in the placebo and selenomethionine groups,” they added.

“Consumption of two Brazil nuts daily is as effective for increasing selenium status and enhancing GPx activity as 100 micrograms of selenium as selenomethionine,” they concluded.

Selenium is understood to boost the body’s antioxidant immune system and may deliver health benefits including reduced risk of some types of cancer and cardiovascular disease and promotion of normal liver function.

In the US the FDA issued a qualified health claim on selenium in 2003, which states: “Selenium may reduce the risk of certain cancers. Some scientific evidence suggests that consumption of selenium may reduce the risk of certain forms of cancer. However, FDA has determined that this evidence is limited and not conclusive.”

Source: American Journal of Clinical Nutrition

February 2008, Volume 87, Pages 379-384

“Brazil nuts: an effective way to improve selenium status”

Authors: C.D. Thomson, A. Chisholm, S.K. McLachlan, J.M. Campbell


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